[Me2Si (Me4C5)NtBu]TiCl2 (Constrained-Geometry Catalyst, hereinafter, will be abbreviated as CGC) was reported by Dow Co. in the early 1990s (U.S. Pat. No. 5,064,802), and excellent aspects of the CGC in the copolymerization reaction of ethylene and alpha-olefin may be summarized in the following two points when compared to commonly known metallocene catalysts: (1) at a high polymerization temperature, high activity is shown and a polymer having high molecular weight is produced, and (2) the copolymerization degree of alpha-olefin having large steric hindrance such as 1-hexene and 1-octene is excellent. In addition, as the various properties of the CGC during performing a polymerization reaction are gradually known, efforts on synthesizing the derivatives thereof and using the same as polymerization catalysts have been actively conducted in academy and industry.
As one approach, the synthesis and the polymerization of a metal compound introducing various bridges instead of a silicon bridge and a nitrogen substituent have been tried. Typical metal compounds known until now are illustrated as the following Compounds (1) to (4) (Chem. Rev. 2003, Vol. 103, pp 283).

The above Compounds (1) to (4) introduce a phosphorous bridge (1), an ethylene or propylene bridge (2), a methylidene bridge (3) or a methylene bridge (4), respectively, instead of the silicon bridge of a CGC structure. However, with the above compounds, improved results on activity, copolymerization performance, etc. could not be obtained by applying to ethylene polymerization or copolymerization with alpha-olefin when compared to those obtained by applying the CGC.
In addition, as another approach, a compound composed of an oxido ligand instead of the amido ligand of the CGC has been synthesized, and some attempts on the polymerization using thereof have been conducted. Examples thereof are summarized as follows.

Compound (5) has been reported by T. J. Marks et al. and is characterized in that a cyclopentadiene (Cp) derivative and an oxido ligand are bridged via an ortho-phenylene group (Organometallics 1997, Vol. 16, pp 5958). A compound having the same bridged group and a polymerization using thereof have been reported by Mu et al. (Organometallics 2004, Vol. 23, pp 540). In addition, the bridging of an indenyl ligand and an oxido ligand by the same ortho-phenylene group has been reported by Rothwell et al. (Chem. Commun. 2003, pp 1034). Compound (6) has been reported by Whitby et al. and is characterized in that a cyclopentadienyl ligand and an oxido ligand are bridged by three carbon atoms (Organometallics 1999, 18, 348). The above catalysts have been reported to show activity in a syndiotactic polystyrene polymerization. Similar compounds have been also reported by Hessen et al. (Organometallics 1998, Vol. 17, pp 1652). Compound (7) has been reported by Rau et al. and is characterized in showing activity in ethylene polymerization and ethylene/1-hexene copolymerization at a high temperature and a high pressure (210° C., 150 MPa) (J. Organomet. Chem. 2000, Vol. 608, pp 71). In addition, the synthesis of a catalyst (8) having a similar structure as that of Compound (7) and a polymerization using the same at a high temperature and a high pressure have been filed by Sumitomo Co. (U.S. Pat. No. 6,548,686). However, not many catalysts among the above attempts are practically applied in commercial plants. Accordingly, a catalyst showing further improved polymerization performance is required, and a simple preparation method of the catalyst is required.